Dispersing of electroconductive particles in webs such as paper, non-woven fabrics, felts and the like has long been practiced to enhance the electroconductivity thereof. Carbon black has been used in such work, albeit the relatively low conductivity has limited severely the applications in which it may be used. Moreover, carbon black is difficult to disperse on the surface of a fiber so a given quantity of the black has, in most systems, not yielded the highest degree of conductivity which was theoretically obtainable in view of the properties of the black pigment.
A substantial amount of work has been done in improving the dispersability of carbon black in aqueous solutions. For example, corrosive type materials like ammonium hydroxide, have been suggested (U.S. Pat. No. 3,152,996 and 3,118,884). Moreover, polyethoxylated amines have been suggested (U.S. Pat. No. 3,565,658).
Some inventors have attempted to increase the conductivity of carbon black or metal pigment-bearing coatings in synthetic polymer films, e.g. on polyester film, by etching the surface of the film with adjuvants contained within the coating composition and thereby achieve better coverage of the film on the coated substrate. Thus, U.S. Pat. No. 3,865,626 reveals the use of such a procedure wherein the etchants are halogenated hydrocarbons phenols, or halogenated lower fatty acids.
In a hindsight evaluation of the invention to be disclosed below, it is also noted that tri-alkyl phosphate and other phosphate-type compounds are known as wetting agents (U.S. Pat. Nos. 2,794,004; 3,138,629; and 3,799,956) in certain applications.